Karen M Hampson

• MPhys PhD FHEA
• Senior Lecturer in Optometry at The University of Manchester

In their pioneering work demonstrating measurement and full correction of the eye’s optical aberrations, Liang, Williams and Miller, [JOSA A 14, 2884 (1997)10.1364/JOSAA.14.002884] showed improvement in visual performance using adaptive optics (AO). Since then, AO visual simulators have been developed to explore the spatial limits to human vision a...

Purpose To determine whether accommodative microfluctuations (AMFs) are affected by the image resolution of the display type being observed. The effect of refractive error is also examined. Methods Twenty participants, (10 myopes and 10 emmetropes) observed a target on four different displays: paper, smartphone, e-reader and visual display unit...

SenAOReFoc is a closed-loop sensorbased adaptive optics (AO) and remote focusing control software that works with a deformable mirror (DM) and a Shack-Hartmann wavefront sensor (SHWS). It is programmed in Python and is open-source on Github https://github.com/jiahecui/SenAOReFoc. A detailed user guide can be found in the Github repository. Here, we...

Adaptive optics (AO) is a technique that corrects for optical aberrations. It was originally proposed to correct for the blurring effect of atmospheric turbulence on images in ground-based telescopes and was instrumental in the work that resulted in the Nobel prize-winning discovery of a supermassive compact object at the centre of our galaxy. When...

We present a compact and contactless reflectance confocal neurosurgical microscope that allows remote-focussing via a deformable mirror for volumetric imaging. Wavefront analysis was performed and remote-focussing was demonstrated in mouse calvaria.

Adaptive optics is being applied widely to a range of microscopies in order to improve imaging quality in the presence of specimen‐induced aberrations. We present here the first implementation of wavefront‐sensorless adaptive optics for a laser‐free, aperture correlation, spinning disk microscope. This widefield method provides confocal‐like optica...

Visual guidance at the cellular level during neurosurgical procedures is essential for complete tumour resection. We present a compact reflectance confocal microscope with a 20 mm working distance that provided <1.2 µm spatial resolution over a 600 µm × 600 µm field of view in the near-infrared region. A physical footprint of 200 mm × 550 mm was ac...

When imaging a sample, inhomogeneities in refractive index cause blur in the image and decrease resolution. Adaptive optics (AO) is a technique that can correct for the resulting aberrations. The most common implementation of AO uses a single deformable mirror that is conjugate to the pupil. A single pupil-conjugate corrective device provides corre...

Specimen induced aberrations can have detrimental effects in all types of high-resolution microscope. In this study, we present a sensorless technique that uses a deformable mirror (DM) to correct aberrations of both the system and sample. Using a laser-free confocal microscope, with patterned disk illumination and detection. The system is based on...

A significant challenge in the production of Earth observation satellites is the precise alignment of the telescope optical components. We have developed a strategy to perform automated alignment of two-mirror telescopes for use in a realistic factory-based setting. A Ritchey–Chrétien telescope was used as an example. The secondary mirror was mount...

The multi-billion dollar Earth observation applications market continues to demand better spatial and temporal resolution; simply put, this means bigger apertures and more satellites. This paper describes a novel deployable telescope that addresses the market needs for a <1m GSD imager in a small launch volume. This system will allow many identical...

Previous studies have shown cognition to have an influence on accommodation. Temporal variation in the accommodative response occurs during the fixation on a stationary target. This constantly shifting response has been called accommodative micro-fluctuations (AMFs). The aim of this study is to determine the effects of increasing task cognitive dem...

When fixating on a stationary object, the power of the eye's lens fluctuates. Studies have suggested that changes in these so-called microfluctuations in accommodation may be a factor in the onset and progression of short-sightedness. Like many physiological signals, the fluctuations in the power of the lens exhibit chaotic behaviour. A breakdown o...

BACKGROUND Variability during normal, healthy gait may appear stochastic but it has deterministic structure. This highlights that variability is not simply the result of random noise in the system, but rather that it reflects sensorimotor modulations of movement that conform to a global underlying structure [1]. This deterministic structure within...

Adaptive optics is a relatively new field, yet it is spreading rapidly and allows new questions to be asked about how the visual system is organized. The editors of this feature issue have posed a series of question to scientists involved in using adaptive optics in vision science. The questions are focused on three main areas. In the first we inve...

We used adaptive optics to determine the effect of monochromatic aberration dynamics on the level of chaos in the accommodation control system. Four participants viewed a stationary target while the dynamics of their aberrations were either left uncorrected, defocus was corrected, or all aberrations except defocus were corrected. Chaos theory analy...

The accommodative response (AR) to changes in dioptric accommodative stimulus (AS) during the latency period and onset of accommodation was investigated. Participants monocularly observed one period of a square wave in AS, with a 2-D baseline and mean, and amplitude 1 D or 2 D; the period of the square wave ranged from 0.10s to 1.00s; both increase...

We used a binocular Shack–Hartmann sensor to measure the aberration dynamics of six participants at a rate of 21 Hz. Chaos theory analysis was used to determine the Lyapunov exponent for the time evolution of the rms wavefront error, accommodation, and each individual Zernike coefficient up to and including the fifth radial order. In all cases ther...

When fixating on a stationary object, the human eye exhibits microfluctuations in accommodation. Changes in the magnitude of these fluctuations reflect changes in the accommodation control system. We used adaptive optics to determine the effect of monochromatic aberration dynamics on the control of steady-state accommodation of four subjects. The s...

Since the characterization of the eye’s monochromatic aberration fluctuations in 2001, the power spectrum has remained the most widely used method for analyzing their dynamics. However, the power spectrum does not capture the complexities of the fluctuations. We measured the monochromatic aberration dynamics of six subjects using a Shack-Hartmann s...

Purpose There is current interest in using adaptive optics (AO) to determining the effect of higher-order monochromatic aberrations on dynamic accommodation control; see for example [1-3]. So far, such studies have been carried out using monocular systems. In real-life situations, however, accommodation occurs binocularly and with associated conver...

Ocular monochromatic aberrations display dynamic behavior even when the eye is fixating on a stationary stimulus. The fluctuations are commonly characterized in the frequency domain using the power spectrum obtained via the Fourier transform. In this paper we used a wavelet-based multifractal analytical approach to provide a more in depth analysis...

Dynamic correction of monochromatic aberrations of the eye is known to affect the accommodation response to a step change in stimulus vergence. We used an adaptive optics system to determine how the temporal location of the correction affects the response. The system consists of a Shack-Hartmann sensor sampling at 20 Hz and a 37-actuator piezoelect...

We used an adaptive optics system to correct the aberration dynamics of five subjects while they fixated on a monochromatic stimulus undergoing sinusoidal vergence changes between 1.5 and 2.5 D, at a temporal frequency of 0.2 Hz. The aberrations were measured at 20 Hz using a Shack–Hartmann sensor and corrected using a 37-actuator deformable mirror...

Manipulation of the eye’s aberrations using adaptive optics (AO) has shown that optical imperfections can affect the dynamic accommodation response. A limitation of current system designs used for such studies is an inability to make direct measurements of the eye’s aberrations during the experiment. We present an AO system which has a dual wavefro...

Background: Accommodation control is mediated by a number of cues, including blur,chromatic aberration and target proximity. Data from wavefront measurements have shown clear shifts in ocular aberrations during increasing accommodative demand, most notably a negative shift in spherical aberration. Work in adaptive optics, where aberrations have be...

It has long been recognised that the optical quality of the human eye is far from diffraction limited. This affects our visual acuity and severely limits the resolution at which images of the living retina can be obtained. Adaptive optics is a technique that can correct for the eye’s aberrations and provide diffraction limited resolution. The origi...

Fluctuations in accommodation have been shown to be correlated in the two eyes of the same subject. However, the dynamic correlation of higher-order aberrations in the frequency domain has not been studied previously. A binocular Shack-Hartmann wavefront sensor is used to measure the ocular wavefront aberrations concurrently in both eyes of six sub...

During steady-state fixation the aberrations of the human eye display dynamic behaviour. It has been suggested that the fluctuations in focus are correlated between both eyes. However, nothing is known about the dynamic correlation between the aberrations other than focus. We have developed an open-view binocular Shack–Hartmann sensor which measure...

Kotulak and Schor have suggested that the accommodative mechanism of the human eye can determine the required response from the changes in retinal image contrast associated with the microfluctuations of accommodation. As other aberrations also display dynamic behaviour, they may too have an input in this self-calibration mechanism. An adaptive opti...

It is now known that defocus is not the only aberration in the eye that exhibits dynamic behavior during fixation. It is currently unknown what effects, if any, the dynamics of these other aberrations have on steady-state accommodation control. We constructed an adaptive optics system to serve as a tool for future investigations in this area. The s...

No The aims of the research may be outlined as follows: to measure the degree of transient axial elongation during the accommodation response in emmetropic and myopic young adults. To evaluate the effect of refractive error and accommodative demand on transient axial elongation of the eye. Axial length of the right eye was measured in 30 emmetropes...

We measured the wavefront aberrations of the eyes of five subjects with a Shack-Hartmann sensor sampling at 21.2 Hz and decomposed the measurements into Zernike aberration terms up to and including the fifth radial order. Coherence function analysis was used to determine the common frequency components between the aberrations within subjects. We fo...

It is fairly well established that the higher-order aberrations of the eye fluctuate over relatively short time periods, but as yet there is no conclusive evidence regarding the origin of these fluctuations. We measured the aberrations and the pulse pressure wave simultaneously for five subjects. The aberrations were measured by using a Shack–Hartm...

Some results concerning the correction loop of an Adaptive Optics (AO) system for the eye are presented. This is part of a project aiming to study the effects of AO on visual performance, using psychophysical methods. The AO system used in the project is presented. It comprises a Shack-Hartmann sensor, which measures the light deformation after a d...